Drought stress is a serious adverse factor limiting growth and productivity of sunflower. Evaluation of defense systems is important for producing resistant cultivars. In this study, some agro-morphological and molecular characteristics of six sunflower lines were evaluated under normal and irrigation at 40 and 60% of field capacity in randomized complete block design (RCBD). The results showed that drought stress affected the measured traits compared to the control. However, the lines showed different responses to the stress. According to the results, C100, C104 and LR55 lines had better growth, yield and drought tolerance indices in water stress conditions. In addition, drought stress increased total protein content of the lines especially resistant ones (C100, C104 and LR55). The protein SDS-PAGE electrophoresis pattern also showed that drought stress caused the accumulation of low molecular weight proteins specially the bands 69.3 and 70.5 kDa were produced in the resistant lines C100, C104 and LR55 under drought stress conditions. Moreover, more protein bands were observed in the resistant lines, C104 and LR55, under normal compared to the stress conditions. It seems that the protein bands 69.3 and 70.5 kDa are resistance-related proteins that were expressed in the tolerant lines. The findings of this study can be useful in sunflower breeding programs for producing resistant cultivars to drought stress.

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